1. Technical Field
The present disclosure generally relates to electronic circuits and, more specifically, to differential input amplifiers. The present disclosure more specifically applies to amplifiers made in bipolar or BiCMOS technology.
2. Description of the Related Art
Amplifiers with a differential input pair are, especially for small signals (on the order of a few tens of millivolts at the input), particularly sensitive to imbalances (offsets) likely to be present in the currents between branches.
One can distinguish so-called random imbalance linked to a mismatch between the components from a so-called systematic imbalance, linked to the amplifier structure (diagram). A random imbalance varies from one chip to the other in circuits of a same wafer while a systematic imbalance is the same for all chips in a same wafer but is sensitive to manufacturing dispersions (variations from one wafer or from one wafer batch to another) as well as to the circuit operating temperature.
The systematic imbalance is due to the sampling, from a single one of the two differential branches, of a current to be amplified to provide the useful signal. This introduces an imbalance in the currents of the two branches, which alters the input signal measurement, and thus the accuracy of the amplification.
The systematic imbalance has long been neglected with respect to the random imbalance. Advances in the correction of random imbalances result in a no longer negligible systematic imbalance, in particular for low-amplitude input signals (with an amplitude lower than a few tens of millivolts).